1. Field of the Invention
The present invention relates to a light emitting device with an LED designed for mainly outdoor use and used as substitute for an incandescent lamp, e.g. a mercury lamp, a halogen lamp or the like.
2. Description of Related Art
A light-emitting diode “LED”, which has advantages such as low power consumption and long life as against a conventional incandescent lamp (for example, a mercury lamp or a halogen lamp), is widely used, because people become more ecology conscious. And people consider that using the LED is one policy for the energy-saving strategies. Particularly, it is highly required to use the LED as an alternate item of the incandescent lamp.
Such a request is not only for an indoor type light emitting device but for a light emitting device for outdoor use, e.g. for lighting a sign board.
A general LED emits light by several volts of DC voltage. Consequently, when a light emitting device with LED is used as substitute for an incandescent lamp, which emits light with utility 100V, 50 or 60 Hz AC voltage, a power circuit for conversion of the utility AC voltage to predetermined volts of DC voltage is required.
On the other hand, the LED emits the light and generates heat at the same time. It is also required to avoid excess high temperature of the power circuit by the heat from the LED.
Particularly, a light emitting device having a plurality of LEDs for increasing the amount of the light generates much more amount of the heat. The protection of the power circuit from the heat is an important issue.
Some protection technologies for the power circuit have been developed. For example, a light emitting device described in Patent Document 1 (Japanese Laid-Open Patent Publication No. 2011-90843) has a board of PST (polybutyleneterephthalate) plastics and heat insulator between the LED and the power circuit. The board and the insulator prevent the heat from conducting to the power circuit.
And a light emitting device described in Patent Document 2 (Japanese Laid-Open Patent Publication No. 2010-157506) has a fan inside its body. By the fan, outside air flows into inside the body through an intake slit provided on a base end of the body. The fan also exhaust the air through an exhaust slit provided on a side surface of light emitting end of the body. The air which receives the heat from the LEDs through the heat sink is exhausted forcibly, with protection of the power circuit.